step

The step event occurs
when the first instruction of a source line is executed. For example, you
can get simple tracing with:

when step { echo $lineno: $line; }; cont

When enabling a step event, you instruct dbx to
single step automatically next time the contcommand is
used.

Note –

The step (and next) events
do not occur upon the termination of the step command.
The step command is implemented in terms of the step event roughly as follows: alias step="when step -temp
{ whereami; stop; }; cont"